Transcript Experimenting with Experimental Brain Science

Experimenting with
Experimental Brain
Science
Dr. Michael Raucci
Education
is not
the filling of a pail,
but the lighting of a fire.
William Butler Yeats
The Art of
Teaching
The
Science of
Teaching
Entertainer
Artist
Philosopher
Teacher
Technician
Scientist
Teacher Duties
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Counselor
Confidant
Advisor
Entertainer
Nurse
Arbitrator
Mediator
Babysitter
Disciplinarian
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Friend
Judge
Supplies Technician
Mother
Ethics/morality model
Hero
Scapegoat
Role-model
Teacher
Goals Today
1) Not to teach you anything
• The idea today is to allow guided exploration
result in self realization and illumination
leading to discussion.
2) We are going to act like really lousy scientists
For fun I want to, when ever possible,
extrapolate what we discover, to what this
might mean if it the process we were
examining worked similarly for other parts of
the brain.
Visual Illusions and Perception
"I'll believe it when I see it with
my own two eyes”
We need to realize that that's not enough.
What is Reality and What is
Perception?
Waterfall
by
M.C. Escher
Is there such a thing as
reality?
The M.C. Escher painting exploits the rules of
depth and proximity and our understanding of
the physical world to create an illusion.
• Is there perception without consciousness?
• Is there anything without perception
• If a tree falls in the woods and there is no one
and nothing to record its happening does it
make a sound?
• Has it even fallen?
• Are there stimuli that we can’t perceive?
Seeing things through the eyes of N
Evolutionary Biologist
Paradox illusion
Brightness
depends on
context
• Luminance in a physical measure the
luminosity of A and B is identical, Brightness
is something your brain constructs. B is
brighter.
• Lateral inhibition is the ability of a neuron to
suppress the output of its neighbor so that
only the most stimulated form our perception
increasing sharpness and contrast
Adelson’s Checker Shadow Illusion
• As with many so-called illusions, this effect
really demonstrates the success rather than
the failure of the visual system. The visual
system is not very good at being a physical
light meter, but that is not its purpose. The
important task is to break the image
information down into meaningful
components, and thereby perceive the nature
of the objects in view.
• Similarly, the eye will compensate for colour
contrast depending on the colour cast of the
surrounding area.
Hermann Grid Illusion
• Hermann grid illusion
• The illusion is characterized by "ghostlike"
grey blobs perceived at the intersections of a
white (or light-colored) grid on a black
background. The grey blobs disappear when
looking directly at an intersection.
Scintillating Grid Illusion
• In this example of lateral inhibition, again the
intensity at a point in the visual system is the
result of not one receptor but multiple.
• Staring at an intersection defeats the illusion
at that intersection
OUCHI IllUSION - apparent motion
• brain of excessive stimulation of a specific
type - brightness, tilt, color, movement, etc.
The theory is that stimuli have individual
dedicated neural paths in the early stages of
visual processing, and that repetitive
stimulation of only one or a few channels
causes a physiological imbalance that alters
perception.
Pop Out
- often avoided by
animal populations
• There is no light source
• Light could be coming from the top or the
bottom
• Your brain makes a choice. It’s a reasonable
choice based upon evolutionary assumptions
• What is it? Why?
Floor tiles at the Basilica of St. John
Lateran in Rome
It's a Lufthansa 747-400 and a United Airlines 757-200 that were on simultaneous
approaches to runways 28L and 28R at San Francisco (SFO). The separation
requirement for flying parallel and simultaneous approaches is 225 meters (738
feet). These two aircraft are at a safe distance for the approaches they are each
flying. Due to the Lufthansa 747 being three times larger than the 757 and being
slightly behind, gives us this illusion.
Shadow bias
• http://gandalf.psych.umn.edu/users/kersten/k
ersten-lab/demos/BallInaBox.mov
• http://www.kyb.tue.mpg.de/bu/demo/blueball/index.html
• http://gandalf.psych.umn.edu/users/kersten/k
ersten-lab/images/kersten-shadow-cine.MOV
Lines and Horizons
Distorting illusion
• This illusion demonstrates the effect of some
simple image processing occurring at the retina
combined with some complex processing in the
cortical cells of the striate cortex. The incoming
image is first filtered by the centre-surround
operator of the retina. The apparent tilt of the
mortar lines is caused by orientation-sensitive
simple cells in the striate cortex. The cells interact
with one another to interpret the diagonal bands
produced by the retina as a single continuous
line, tilted in the direction of the diagonal bands.
• The imaginary white triangle is one instance in
which brain fills in some logical ingredients to
complete the picture
• Clouds – spotting recognizable shapes in clouds
• Jesus grilled –cheese sandwiches
• Fashion- the goal of some fashions is by
concealing the exact shapes of the wearers body
they give ample room for the brain to imagine
the idealized representation it expects
• The brain has a need to see familiar simple objects and
has a tendency to create a "whole" image from
individual elements…Gestalt
• Another explanation of the is based in evolutionary
psychology and the fact that in order to survive it was
important to see form and edges. The use of
perceptual organization to create meaning out of
stimuli is the principle behind other well-known
illusions including impossible objects.
• Our brain makes sense of shapes and symbols putting
them together like a jigsaw puzzle, formulating that
which isn't there to that which is believable.
Filling In
• One common fallacy is to assume there is an image
inside your eyeball, the optical image, exciting
photoreceptors on your retina and then that image is
transmitted faithfully along a cable called the optic
nerve and displayed on a screen called the visual
cortex. Now this is obviously a logical fallacy because if
you have a screen and an image displayed on a screen
in the brain, then you need another little chap in there
watching that image, and there is no little chap in your
head. And if you think about it, that wouldn't solve the
problem either because then you'd need another little
guy in his head looking at the image in his brain …….
• So the first thing you have to do to understand
perception is to get rid of the idea of images in the
brain and think instead of transforms or symbolic
representations of objects and events in the external
world. Just as little squiggles of ink, print or writing, or
dots and dashes in the Morse code can symbolize or
represent something even they don't physically
resemble what they are representing, similarly the
action of nerve cells in your brain, the patterns of
firing, represent objects and events in the external
world even though they don't in any way resemble
what's out there in the world.
Ignoring Effect
• Not only can your bran bring things into existence it can
also block out the things it wants to ignore.
• Brain is hard-wired to focus attention on threatening
sounds and sights. To assist the brain filters out repetitive,
unchanging stimuli like a whirring air conditioner or the
rocking of a boat at sea.
• At the lowest level, constantly stimulated neurons
temporarily stop firing. (For this reason, your eyes jitter
back and forth even when you hold your gaze steady. If
they didn’t, the same neurons would always be stimulated
by the sight in front of you. They’d get tired out, stop firing
and everything would fade into blackness
• Adpatation to different levels of brightness
• DOORWAY experiment – pushing hands
against sides of door – brain becomes
accustomed to needing extra effort to keep
arms up .
• Walk away with arms ni same position.
• Sensation of arms drifting upwards
• Ignoring smells - hard not to – p 87 manual
Pattern Completion and Ambiguity
Ambiguous illusion
To make sense of the world it is necessary to
organize incoming sensations into information
which is meaningful.Gestalt psychologists
believe one way this is done is by perceiving
individual sensory stimuli as a meaningful
whole.[2] Gestalt organization can be used to
explain many illusions including the Duck-Rabbit
illusion where the image as a whole switches
back and forth from being a duck then being a
rabbit and why in the figure-ground illusion the
figure and ground are reversible.
Priming and Pattern Recognition
• Rorsach
• Hard priming
• Soft priming
• Primacy contributers
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Time proximity
Implicit
Humans
danger
• When looking at the inkblot most of us are aware
of the imaginative power we’re investing
however there are cases where your brain
performs the same task without you realizing the
creative leap its taking.
• Have you ever thought you heard the phone
ringing or a person calling your name while
running a noisy appliance like a vacuum. This
effect is spurred by the brain’s pattern matching
system
Peripheral Vision
• Color tabs
Motion After-effect
• http://psylux.psych.tudresden.de/i1/kaw/diverses%20Material/ww
w.illusionworks.com/html/motion_aftereffect.
html
Stepping Feet
• http://psy2.ucsd.edu/~sanstis/Foot.html
• http://www.michaelbach.de/ot/mot_feet_lin/
Flash-lag
• http://www.michaelbach.de/ot/mot_flashlag1
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The flash lag illusion or flash-lag effect is a visual illusion wherein a flash and a moving object that appear in the same location
are perceived to be displaced from one another (MacKay, 1958; Nijhawan, 1994). Several explanations for this simple illusion
have been explored in the neuroscience literature.
Contents
[hide]
1 Motion extrapolation
2 Latency difference
3 Motion integration and postdiction
4 See also
5 References
6 External links
[edit] Motion extrapolation
The first proposed explanation for the flash-lag effect is that the visual system is predictive, accounting for neural delays by
extrapolating the trajectory of a moving stimulus into the future (Nijhawan, 1994; Khurana and Nijhawan, 1995). In other words,
when light from a moving object hits the retina, a certain amount of time is required before the object is perceived. In that
time, the object has moved to a new location in the world. The motion extrapolation hypothesis asserts that the visual system
will take care of such delays by extrapolating the position of moving objects forward in time.
[edit] Latency difference
A second proposed explanation is that the visual system processes moving objects more quickly than flashed objects. This
latency-difference hypothesis asserts that by the time the flashed object is processed, the moving object has already moved to
a new position (Baldo and Klein, 1995; Whitney & Murakami, 1998; Purushothaman et al., 1998). The latency-difference
proposal tacitly rests on the assumption that awareness (what the subject reports) is an on-line phenomenon, coming about as
soon as a stimulus reaches its "perceptual end-point" (Zeki & Bartels, 1998).
[edit] Motion integration and postdiction
Eagleman & Sejnowski (2000abc) proposed a third alternative: visual awareness is neither predictive nor on-line, but is instead
postdictive, such that the percept attributed to the time of the flash is a function of events that happen in the ~80 msec
following the flash. This postdictive framework is consistent with findings in other fields, such as backward masking in visual
psychophysics (Bachmann, 1994), or the Color Phi phenomenon (Kolers & von Grunau, 1976). In backward masking, a stimulus
followed in rapid succession by a second stimulus can block or modify the perception of the first one. In the color phi
phenomenon, 2 colored dots presented sequentially within a small time and distance will appear to have changed color in the
middle of their apparent trajectory. Since the viewer cannot know what the color of the second dot will be until having seen the
second dot, the only explanation is that the conscious percept attributed to the 'trajectory' of the dots is formed after the
second dot has 'arrived' at its destination. Eagleman & Sejnowski found that the perception attributed to the time of the flash
depends on events in the next ~80 msec after the flash. In this way, they drew a correspondence between the flash-lag effect
and the Fröhlich effect (Fröhlich, 1923), wherein the first position of a moving object entering a window is misperceived.
Movement Distortions & Illusions
Rotating Snakes Illusion
• After each saccade, the previously viewed
dots aren’t quite where your brain expects
them to be, and so it assumes that they’ve
shifted ever so slightly to the side. This
creates the impression of motion
eyetracking
http://www.poynterextra.org/eyetrack2004/
Messing with your Brain
Sit so that the white surface or wall is on your right. Hold the bottom of the mirror with your left hand, and put the mirror edge against your nose so that
the reflecting surface of the mirror faces sideways, toward the white surface.
While keeping the mirror edge against your nose, rotate the mirror so that your right eye sees just the reflection of the white wall, while your left eye
looks forward at the face of a friend who is sitting a couple of feet away (see diagram). Move your hand in front of the white surface as if passing a
blackboard eraser over the surface. Watch as parts of your friend's face disappear.
It will help if your friend is sitting very still against a plain, light-colored background. You should also try to keep your own head as still as possible.
If you have trouble seeing your friend's face disappear, one of your eyes might be stronger than the other. Try the experiment again, but this time switch
the eye you use to look at the person and the eye you use to look at the wall.
Individuals vary greatly in their ability to perceive this effect; a few people may never succeed in observing it. You may have to try this several times.
Don't give up too soon! Give yourself time to see the effect.
Normally, your two eyes see very slightly different pictures of the world around you. Your brain analyzes these two pictures and then combines them to
create a single, three-dimensional image.
In this Snack, the mirror lets your eyes see two very different views. One eye looks straight ahead at another person, while the other eye looks at the
white wall or screen and your moving hand. Your brain tries to put together a picture that makes sense by selecting bits and pieces from both views.
Your brain is very sensitive to changes and motion. Since the other person is sitting very still, your brain emphasizes the information coming from the
moving hand, and parts of the person's face disappear. No one knows how or why parts of the face sometimes remain, but the eyes and the mouth seem
to be the last features to disappear. The lingering mouth gives rise to the name of this exhibit.
The name for this exhibit derives from the Cheshire Cat in Lewis Carroll's story Alice's Adventures in Wonderland. The cat disappears, leaving behind only
its smile.
Hollow Face Illusion
Hollow Face Illusion
• Says Richard Gregory, "The strong visual bias of
favouring seeing a hollow mask as a normal convex
face (figure 1), is evidence for the power of top-down
knowledge for vision (Gregory 1970). This bias of
seeing faces as convex is so strong it counters
competing monocular depth cues, such as shading and
shadows, and also very considerable unambiguous
information from the two eyes signaling
stereoscopically that the object is hollow. (Lighting a
concave face from below to reverse the shading cues
making them closer to those of a convex face lit from
above can reinforce the illusion.)
• The brain is a pattern matching machine. You
can make it more conservative in which it will
miss things or you can make it more
aggressive in which it will occasionallly invent
them. The brain does both, although it is
more likely to imagine something into
existence than block it out because this proves
to be the safer survival strategy
Your Brain – the missing manual
• The human brain was cobbled together over vast ceans
of time , it’s no surrise that its parts don’t always work
in harmony. For example, a sudden scare can cause
your brain to briefly shut down its higher level
functioning and respond with the survival strategies
that are coded at a deeper level.
• Similar battle with perception of optical illusions.
• Last major change in brain 100,000 years ago.
• So how well does the brain adapt to fast cars, fast food,
and chronic stress
• Overstimulating part of the brain’s visual
processing system..like the sfterimage you get
when you stare into the sun
• Part of the brain’s strategy when picking out
shapes involvrs emphasizing edges and
contrasts.
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It has long been apparent that the perceived brightness of objects does not correspond in any simple way to their luminance (i.e., to the measured intensity of light corrected for the spectral sensitivity of the
human visual system) (Figure 1A). In particular, two surfaces returning the same amount of light to the eye can look differently bright if the surfaces are observed in different contexts, a phenomenon called
simultaneous brightness contrast (most psychologists prefer to call this 'lightness' contrast to distinguish the appearance of surfaces that reflect light from the appearance of endogenous sources of light; for
present purposes, this distinction is not critical, and the term 'brightness' is used here in its ordinary meaning of perceived intensity).
The explanation of this remarkable effect found in many textbooks is predicated on lateral interactions among retinal ganglion cells or other lower order visual neurons, which demonstrably cause distorted
rates of neuronal firing at contrast boundaries, presumably to enhance the detection of edges (Figure 1B). This interpretation implies that the relative intensities perceived in response to such stimuli are, in
effect, 'readouts' of the relative firing rate of neurons at the input stages of the visual. On this basis, any target predominantly surrounded by an area of higher luminance should look darker than the same
target predominantly surrounded by an area of lower luminance.
Figure 1 « Close
Figure 1 / Standard demonstration of simultaneous brightness contrast, and the conventional explanation of this effect. A) A target (the diamond) on a less luminant background (left) is perceived as being
brighter than the same target on a more luminant background (right), even though the two targets are physical identical, and appear so if both are presented on the same background (as shown above). B)
Diagram of the usual explanation of this phenomenon, based on the center-surround receptive field properties of retinal ganglion cells. the center-surround receptive field organization of input level neurons
will, as illustrated here, cause less lateral inibition, and therefore more signal passed centrally from high contrast boundaries than from lower ones.
Despite the apparent concordance of perception and retinal physiology in this instance, a number of observations indicate that identical targets embedded in scenes that have exactly the same local contrast
relationships with their surrounds can nonetheless look differently bright (Figure 2). Indeed it is even possible to construct stimuli in which a target in a predominantly higher luminance surround looks brighter
than an identical target in a predominantly lower luminance surround (Figure 2B). How, then, can these seeming contradictions in the relationship of luminance and brightness be explained?
Figure 2 « Close
Figure 2 / Evidence that distorted neuronal responses to local contrast (Figure 1B) cannot explain simultaneous brightness contrast. A) In the Wertheimer-Benary stimulus, two equiluminant targets (the gray
triangles) elicit different sensations of brightness despite having the same local contrast relationships (for most observers the upper triangle looks slightly brighter/lighter than the lower one). B) White's
illusion is particularly interesting because it generates a perception of relative brightness that is similar to the sensations elicited in Figure 1A, despite the fact that the local contrast of the patches (set inset
left) is more or less opposite the standard brightness contrast stimulus shown in Figure 1A. Thus, the targets that appear brighter (the patches on the left) are mainly surrounded by areas of higher luminance,
whereas the targets that appear darker are surrounded mainly by areas of lower luminance. C) Differences in lightness/brightness of equiluminant targets in the absence of any differences at all in local
luminance contrast. Top panel - Light and dark surrounds with equiluminant test diamonds on the adjacent faces of a cube. Middle panel - The same cube rotated 180°. Bottom panel - Graph showing the
average adjustment made by observers to equalize the brightness of the two test targets in the upper and middle panels.
In terms of a wholly empirical strategy of vision, the explanation of the difference in perceived brightness of the two equiluminant targets in Figure 1A and in this Demonstration is summarized in Figure 3
(Williams et al, 1998a and b; see also Lotto and Purves, 1999). Since the amount of light returned to eye from any portion of a scene depends on both the illumination of the relevant surfaces and their
reflectances (among other factors), the equiluminant returns from the targets are inherently ambiguous. Such stimuli will often have been generated by similarly reflective surfaces on differently reflective
surrounds under the same illuminant; the same luminance profiles, however, will often have signified differently reflective target surfaces under different amounts of illumination.
Figure 3 « Close
Figure 3 / A probabilistic explanation of simultaneous brightness contrast effects. A) A standard simultaneous brightness contrast stimulus. B and C) Cartoons illustrating the two major categorical sources of
the stimulus in (A). The different lightness/brightness of the two identical targets in (A) is seen because the response to the stimulus incorporates all its possible sources in proportion to their past frequency of
occurrence, which differs in natural scenes.
Since dealing successfully with this or any stimulus depends on responding appropriately to the sources of the retinal stimulus rather than the stimulus as such, the visual system can only solve this problem on
the basis of past experience. If this idea is correct, then to the extent that the stimulus is consistent with similarly reflective target surfaces under the same illuminant, the targets will tend to appear similarly
bright. However, in so far as the stimulus is consistent with the past experience of the visual system with differently reflective objects in different levels of illumination, the targets will tend to appear
differently bright. Because the standard simultaneous brightness contrast stimulus is consistent with either of these possible sources, the pattern of neural activity elicited - that is, the percept experienced
when looking at the stimulus in Figure 1A or Figure 3A (or the related demonstrations) - is a manifestation of both possibilities (and indeed all of the many other possibilities not illustrated) in proportion to
their relative frequency of occurrence in past experience with stimuli of this general sort.
In support of this explanation, crafting the stimulus in this Demonstration to be more consistent with differently reflective surfaces in different illuminants increases the 'illusion' of simultaneous brightness
contrast (see Demonstration, for example), whereas making the stimulus less consistent with this possibility, and more consistent with the source being similar reflective objects under similar illuminants
causes the targets to appear more similar, even if all the luminance relationships in the scene are preserved. Other more complex examples that support this interpretation of how lightness/brightness
percepts are generated are found in this Demonstration.
References
Lotto RB, Purves D (1999) The effects of color on brightness. Nat Neurosc 2: 1010-1014.
Purves D, Lotto B (2002) Why We See What We Do: An Empirical Theory of Vision. Sunderland, MA: Sinauer Associates.
Purves D, Lotto R B, Williams SM, Nundy S, and Yang, Z (2001) Why we see things the way we do: Evidence for a wholly empirical strategy of vision. Philos. Trans. Roy. Soc., 356:285-297.
Purves D, Williams MS, Nundy S, Lotto RB (2004) Perceiving the intensity of light. Psychological Rev. Vol 111: 142-158.
Williams SM, McCoy AN, Purves D (1998a) The influence of depicted illumination on perceived brightness. Proc Natl Acad Sci USA 95:13296-13300.
Williams SM, McCoy AN, Purves D (1998b) An empirical explanation of brightness. Proc Natl Acad Sci USA 95:13301-13306.
Yang Z, Purves D (2004) The statistical structure of natural light patterns determines perceived light intensity. Proc Natl Acad Sci 101: 8745-8750.
• The brain is a pattern matching machine. You
can make it more conservative in which it will
miss things or you can make it more
aggressive in which it will occasionallly invent
them. The brain does both, although it more
likely to imagine something into existence
than block it out because this proves to be the
safer survival strategy
• The imaginary white triangle is one instance in
which brain fills in some logiical ingredients to
complete the picture
• Clouds – spotting recognizable shapes in clouds
• Jesus grilled –cheese sandwiches
• Fashion- the goal of some fashions is by
concealing the exact shapes of the wearers body
they give ample room for the brain to imagine
the idealized representation it expects
• When looking at the inkblot most of us are aware
of the imaginative power we’re investing
however there are cases where your brain
performs the same task without you realizing the
creative leap its taking.
• Have you ever thuoght you heard the phone
ringing or a person calling your nam while
running a noisy appliance like a vacuum. This
effect is spurred by the brain’s pattern matching
system
Ignoring Effect
• Not only can your bran bring things into existence it can
also block out the things it wants to ignore.
• Brain is hard-wired to focus attention on threatening
sounds and sights. To assist the brain filters out repetitive,
unchanging stimuli like a whirring air conditioner or the
rocking of a boat at sea.
• At the lowest level, constantly stimulated neurons
temporarily stop firing. (For this reason, your eyes jitter
back and forth even when you hold your gaze steady. If
they didn’t, the same neurons would always be stimulated
by the sight in front of you. They’d get tired out, stop firing
and everything would fade into blackness
• Adpatation to different levels of brightness
• DOORWAY experiment – pushing hands
against sides of door – brain becomes
accustomed to needing extra effort to keep
arms up .
• Walk away with arms ni same position.
• Sensation of arms drifting upwards
• Ignoring smells - hard not to – p 87 manual
• Theres a group of people gathered indoors in discussio
there appears to be a window on the left above one
woman.
• These “obvious facts” aren’t quite as obvious to people ith
differernt expereinces and different assumptions
engravedd ontheir brains.
• When shown to East Africans, nearly all of them said the
woman on the left was balancing a box on her head and
the corner of the room was a tree.
• As a Westerner who has spent much of life indoors you
interpret things differerntly
• Same holds true for the faces-vase illusion
• Overstimulating part of the brain’s visual
processing system..like the afterimage you get
when you stare into the sun
• Part of the brain’s strategy when picking out
shapes involves emphasizing edges and
contrasts.
Discussion Points
• What is reality
• How can 2 people experience different
realities
• Can I influence another person’s perception of
reality. How?
• What are some bias that are hard-wired into
the brain?
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Flashdrive
Gathering for gardner copies
Rubber hand
Print out discussion points
Mirror Box
Mirrors